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Analysis of Acoustic Absorption with Extended Liner Reaction and Grazing Flow
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. Scania.ORCID iD: 0000-0003-1604-8263
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Acoustic absorbing liners are efficient and commonly used measures to reduce sound levels in many fields of application. The sound reducingperformance of the liners is dependent on the acoustic state, defined by e.g. the flow and sound field interacting with the liner. To enable liner optimization the impact of these factors on the liner performance must be predictable. Studies of the impact of these factors were performed with existing experimental, analytical and numerical methods at low Mach number flows and material used in truck engine compartments. The study showed significant impact of both flow and sound field onthe liner performance. The size of the impact of the flow depends on which of the existing methods and models that was used, implying theneed of complementary methods. A new numerical method to model the boundary layer effect was for this reason developed in this work. The method was shown to predict the impact of flow correctly compared to the Pridmore-Brown solution and the method was computationally efficient. The sound reducing performance of a liner exposed to complex sound field and grazing flow can be predicted using existing methods together with the new proposed method. Extra care has to be taken when bulk reacting liners are considered since additional complications compared to locally reacting surfaces occur in presence the of grazing flow.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , x, 46 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2013:42
Keyword [en]
Sound absorption, acoustic lining, non-locally reacting, boundary layer, grazing flow, sound field, transfer matrix method
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-128711OAI: oai:DiVA.org:kth-128711DiVA: diva2:648442
Presentation
2013-09-27, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20130916

Available from: 2013-09-16 Created: 2013-09-16 Last updated: 2013-09-16Bibliographically approved
List of papers
1. On sound absorbing characteristics and suitable measurement methods
Open this publication in new window or tab >>On sound absorbing characteristics and suitable measurement methods
2012 (English)In: SAE Technical Paper 2012-01-1534, 2012, Society of Automotive Engineers, 2012Conference paper, Published paper (Refereed)
Abstract [en]

Noise encapsulations are widely used in automotive industry to enclose noise sources, such as e.g. the engine or the gearbox, to reduce externally radiated noise. The sound absorption factor of the material on the inside of the noise encapsulation is obviously vital for the sound attenuation. This parameter is in most cases determined experimentally for which there are several methods. The results received from the various methods may vary as different acoustic states are examined and thus influence the choice of method. The absorption factor is crucial since it is used in specifications to material manufacturers as well as being an input parameter in modeling the performance of the noise shield e.g. during a pass-by noise test.

In this paper, two standardized measurement methods along with a third, non-standardized method, are applied to determine the properties of an absorbing material used in a commercial noise encapsulation. The methods are based on normal-, random- and oblique incident sound waves. The first and the last methods are based on measuring the acoustic impedance from which the absorption can be calculated while the random incidence method measures the absorption directly. The results retrieved from the three methods are compared and discussed in the light of the differences between them. This paper clarifies the differences and gives a practical guidance for the choice of measurement method and the use of the different absorption factors in modeling.

Place, publisher, year, edition, pages
Society of Automotive Engineers, 2012
Keyword
Sound absorption coefficient, surface impedance, local reaction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128552 (URN)10.4271/2012-01-1534 (DOI)2-s2.0-84877167175 (Scopus ID)
Conference
th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2012; Graz; Austria; 13 June 2012 through 15 June 2012
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-03-11Bibliographically approved
2. On variation of absorption factor due to measurement method and correction factors for conversion between methods
Open this publication in new window or tab >>On variation of absorption factor due to measurement method and correction factors for conversion between methods
2012 (English)In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, Volume 11, 2012, Institute of noise control engineering , 2012, 9343-9350 p.Conference paper, Published paper (Other academic)
Abstract [en]

Sound absorbing materials are used in many applications to reduce sound, and their soundabsorbing characteristics are most often determined experimentally since theoreticaldetermination is difficult. Sound absorption factors are used in material specifications aswell as input to numerical simulations.Several methods for experimental determination of the absorption factor exist, two of themstandardized and frequently used. It is commonly known that the absorption factorobtained by these two methods differs as different sound fields are prescribed by thestandards. However, the size of the differences has not been so well described. Due to thisdifference, the choice of method is critical in order to avoid errors in simulations andspecifications of material properties.Experimental determination of absorption factors for three commonly used absorbers wasperformed, resulting in significant differences between the two methods. Correction factorsto compensate the absorption factor determined at one acoustic state and used in anotherare given. Theory verifying the differences is also presented.

Place, publisher, year, edition, pages
Institute of noise control engineering, 2012
Keyword
Sound absorption coefficient, measurements
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128557 (URN)2-s2.0-84883591764 (Scopus ID)978-162748560-9 (ISBN)
Conference
41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, New York, NY; United States; 19 August 2012 through 22 August 2012
Note

References: Färm, A., Boij, S., Glav, R., On sound absorbing characteristics and suitable measurement methods (2012) Proceedings of the 7 International Styrian Noise, Vibration and Harshness Congress; (2003) Acoustics - Measurement of Sound Absorption in a Reverberation Room, , ISO 354; (1996) Acoustics - Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes - Part 1: Method Using Standing Wave Ratio, , International standard ISO 10534-1; Delany, M.E., Bazley, E.N., Acoustic properties of fibrous absorbent materials (1970) Applied Acoustics, 3, pp. 105-116; Corcos, G.M., The structure of the turbulent pressure field in boundary layer flows J. of Fluid Mechanics, 18, p. 1964; Biot, M.A., Generalized theory of acoustic propagation in porous dissipative media (1962) Journal of the Acoustical Society of America, 34 (9), pp. 1254-1264; Attenborough, K., Acoustical characterization of porous materials (1982) Physics Reports, 82 (3), pp. 179-227; Sastry, J.S., Munjal, M.L., A transfer matrix approach for evaluation of the response of a multi-layer infinite plate to a two-dimensional pressure excitation (1995) Journal of Sound and Vibration, 182 (1), pp. 109-128

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-02-15Bibliographically approved
3. The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows
Open this publication in new window or tab >>The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows
2013 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Sound absorbing linings are effective noise treatments in many applications in order to meet noise emission requirements. Stricter noise requirements set harder demands on the performance of the liners, why better prediction models of their performance have to be developed. As of today, several models to predict the sound reducing properties in the presence of flow exist and are shown to give diverging absorption properties for locally reacting liners exposed to high Mach number flows. The effect of flow on absorption properties is often seen as an issue that only needs to be addressed at high Mach number flows. In this paper, the existing models are applied to bulk reacting liners exposed to low Mach number flows and the resulting absorption coefficients are compared. Predictions of absorption coefficients clearly show that the effect of flow needs to be considered also at low Mach number flows and that the difference between the prediction models is indeed significant at low Mach number flows. This shows the importance in choosing the correct model for a specific application in order to avoid introducing erroneous prediction on the effect of flow. This study thus gives well-grounded evidence of the importance to include flow effects in modeling of sound absorptive linings even at low Mach number flows.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2013
Keyword
Sound absorption, surface impedance, grazing flow, liners
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128559 (URN)2-s2.0-84883681935 (Scopus ID)
Conference
19th AIAA/CEAS Aeroacoustics Conference, 27-29 May, 2013, Berlin, Germany
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-11-25Bibliographically approved
4. An Extended Transfer Matrix Approach to Model the Effect of Boundary Layers on Acoustic Linings
Open this publication in new window or tab >>An Extended Transfer Matrix Approach to Model the Effect of Boundary Layers on Acoustic Linings
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sound absorbing materials exposed to grazing flow experience a change in the surface properties due to the boundary layer developed above the surface. The effect of this boundary layer is significant even for fairly low Mach numbers, and several attempts to find analytical models to describe this effect have previously been made. This paper proposes a numerical discretization method, based on the classic transfer matrix approach to model the boundary layer effect. The method includes the time averaged flow velocity gradients of the boundary layer, which is shown to be essential in order to obtain convergence to the correct solution. The method is found to predict the effect of the boundary layer on the surface properties correctly compared to previous numerical solutions. The proposed method is simple to implement, and benets from a fast convergence relative to other numerical methods.

Keyword
grazing flow, surface impedance, sound absorption
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128560 (URN)
Note

QS2013

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2013-09-16Bibliographically approved

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